The investigation is said to concern her time as a solicitor with the Hamilton Burns WS firm.

Opposition parties have repeated their calls for Ms Ahmed-Sheikh to be suspended.

But speaking on the election trail in Musselburgh, Ms Sturgeon told BBC Scotland that the Law Society investigates "many, many complaints about solicitors every year".

She added: "Just because a complaint is raised and an investigation is under way does not mean there has been wrongdoing on the part of the lawyer concerned.

"It's important that these matters are fully and robustly investigated, that's part of the role of the Law Society, so they should be allowed to get on with that investigation and come to a conclusion."

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Nicola Sturgeon served customers in a coffee shop during a campaign visit to Musselburgh

Ms Ahmed-Sheikh won the Ochil and South Perthshire seat with a majority of just over 10,000 at the 2015 general election.

She will be standing for re-election on 8 June, when the other candidates will be Luke Graham of the Scottish Conservatives, Joanne Ross of Scottish Labour and Iliyan Stefanov of the Scottish Liberal Democrats.